Voltage regulation with temperature compensation



p 1963 R. P. SCHNEIDER ETAL 3,103,617

VOLTAGE REGULATION WITH TEMPERATURE COMPENSATION Filed May 6, 1958 I- l-8* W *8 2 N P3 g IL/ fil g n W i 8 07 L0 --'vs: (I) (0 r0 to 1| 8 'v6 zN w n i M a INVENTORS.

ROBERT P. SCHNEIDER ALBERTJ. MEYERHOFF f BY PHILIP E. SHAFER 1- AGENTUnited States Patent "ice 3,103,617 VOLTAGE REGULATION WITH TEMPERATURECOMPENSATION Robert P. Schneider, King of Prussia, Albert J. Meyerhotf,Wynnewood, and Philip E. Shafer, Holmes, Pa., assignors to BurroughsCorporation, Detroit, Mich., a corporation of Michigan Filed May 6,1958, Ser. No. 733,346

14 Claims. (Cl. 323-22) This invention relates to direct current powersupplies and more particularly to low voltage power supplies utilizingtransistorized balanced amplifiers.

Transistor regulators have several advantageous characteristics such aslow voltage and power requirements, fast starting time and long termreliability. However, there are two inherently poor characteristics inthe transistor voltage regulator as compared'with vacuum tuberegulators. These poor characteristics generally are feedback responsetime and the variation of transistor parameters with temperature.

It is, therefore, an object of our invention to provide 3,] 03,6 1 7,Patented Sept. 10, 1963 the positive output terminal 19 of theregulator. The base 41 of the first NPN transistor is connected to theWiper 43 of the potentiometer 45. The resistance portion 47 of thepotentiometer 45 is connected on one side to the negative line 25through resistor 49. The other side of the resistance portion 47 isconnected to the a low voltage direct current power supply having verylated output voltage with little or no change in regulation due tochanges in temperature and which is capable of being subjected torelatively rough treatment.

The foregoing objects are accomplished in our inven tion by theme ofregulating type semi-conductors along with amplifying typesemi-conductors arranged in such a manner that the temperature variationin the parameters of the several semi-conductors in the regulatingcircuit counteract each other. so as to provide a resultant of no changein output voltage with a change in temperature.

Generally, this is accomplished by providing in the line of anunregulated direct current power supply, a power transistor capable ofaltering the potential on the line by changing its impedance. The methodof varying this impedance is by the use of three transistors in afeedback circuit. The first of thesetransistors is subjected to thechanges in output voltage through a zener diode. The output of thisfirst transistor determines the operation 'ofthe second which functionsinversely as the first. The current of the second transistor is ap:plied to a third transistor which acts as the driver for the powerdevice. A fourth transistor is provided to assure operation current ofthe second transistor equal to that of the first. Other features of thecircuit will be made clear in the detailed description which follows.

The drawing is a schematic diagram of one embodiment of the invention.

The positive terminal 11 of an unregulated power supply is connected tothe. emitter 13 of a PNP power transistor 15. The collector 17 of thepower transistor is connected to the positive output terminal 19 of theregulator. The positive output terminal 19 is connected to a load device21, the other side of which is connected to the negative output terminal23 of the regulator which is directly connected through the line 25 tothe negative input terminal 27.

The emitter 29 of a first NPN transistor 31 and the emitter 33 ot asecond NPN transistor 35 are connected to the line 25 of the devicethrough a resistor 37. The collector 390i the first NPN transistor isconnected to positive regulated output terminal through one or morezener diodes 51 arranged in reverse zfashion in the line; that is, withtheir'cathodes connected toward the positive line. The collector53 ofthe transistor 35 is connected to the base 55 of the PNP, transistor 57.The collector 59 of the transistor 57 is connected to the negative line25 through the resistor 61. The emitter 63 of the transistor '57 isconnected to the'base 65 of the transistor 15 through the zener diode67. The zener diode 67 is connected with its cathode toward the base 65of the transistor .15. The base 65- of the transistor 15 is connected toa source of potential 66, more positive than the voltage at the positiveterminal 11, through the resistor 68. The emitter 63 of the transistor57 is also connected to the unregulated positive terminal 11 through theresistor 69.

The base 71 of the transistor 35 is connected to the unregulatedpositive terminal 11 through the resistor 73. The base 71 of thetransistor 35 is also connected to the negative line 25 through one ormore zener diodes 75.

These zener diodes like the previous zener diodes 51 are connected inreverse fashion; that is, with their anodes toward the negative line 25.The base 71 of the transistor 35 is also connected to the regulatedpositive terminal 19 through the diode 77, connected in normal fashion,and resistor 79.

Another PNP transistor 81 has its collector '83 connected to thecollector 53 of the NPN transistor 35. The emitter 85 of the transistor81 is connected to the unregulated positive terminal 11 through theresistor 87. The base 89 of transistor 81 is connected tothe negativeline 25 through the resistor 91. The base 89 of the transistor 81 isalso connected to the unregulated positive terminal 11 through the zenerdiode 93, which like the other zener diodes, is connected in reverse(fashion.

A resistor is connected from the unregulated positive terminal 11 to theemitters 29 and 33 of the transistors 3-1 and 35. A capacitor 97 isconnected across the zener diodes 51. Another capacitor 99' is connectedacross the zener diodes 75. Still another capacitor 101 is connectedfrom the regulated positive terminal 19 to the negative terminal 23.

The operation of the circuit is as follows:

An unregulated source of voltage is applied across the input terminals11 and 27. The potential is applied across the series circuit includingthe zener diode 93 and the resistor 91 thereby providing a voltagedivider network with a constant voltage drop across the zener diode 93.The positive potential is also applied to the emitter 85 of the PNPtransistor 81 through a resistor 87. The junction of the voltage dividernetwork including the zener diode 93 is connected to the base 89 of thetransistor 81. Since there is a voltage drop across the zener diode 9'3and none across the resistor 87, a negative bias is applied to the baseof the PNP transistor 81 and current tends to flow through thetransistor 81. The positive potential is also applied/to the base 71 ofthe NPN transistor 35 through resistor 73. The collector 53 ot the NPNtransistor 35 is connected to the collector 83 of the PNP transistor 81.With this arrangement current now flows from the negative terminal 27through the line25, the

i the base 71 of transistor 35 through resistor 73 to the positiveterminal 1'1. base current, in addition to allowing the collectorcurrent of transistor 81 to flow through the transistor 35 also providesfor additional starting current. This additional current is supplied tothe base 55 of transistor 57 to the emitter 63 of transistor '57,through the zener diode 67, the base 65 of the .tran- Upon theinitiation of current through the powertransistor 15, the voltage outputterminal 19 will become positive in potential. Consequently, the currentwill flow from the negative line 25through'the resistor 49, thepotentiometer 45 and the zones diodes" 51 to the power transistor 15.Upon-the flow of current through circuit, the wiper -43 on thepotentiometer and the base 41 of transistor 31 will become positive andalso since the voltage output terminal .19. ispositive, the collectorConsex 39 of the transistor 31 will become positive; quently, thetransistor 31 will oommence to conduct in its normal fashion.

The collector, current. of the power transistor 15 is delivered tothepositive output terminal 19. The load 21 issupplied from the outputterminals 19 and 23. The

output voltage is applied across a series circuit the zener diodes 51,potentiometer 45 andthe resistor 49. Since the voltage drop across thezener diodes is constant due to the nature of the diodes, any change involtage across the potentiometer 45 and the resistor 49. would decrease;'lhis deereasein voltage will be applied to the base 41 of the. NPNtransistor 31 thereby causing that a transistor to conduct a lesseramount than by its nominal operation. The smaller emitter current fromthe tran sistor 31 when applied to the resistor 37 will cause a smallervoltage-drop across the resistor 37 thereby making the emitter33-of'triansistor 35 more negative than it had been in nominaloperation. The voltage at the base 71 of the transistor 35 is held"constant by the zener diodes 75. The'more negative emittercauses thetransistor 35 to increase itsconductance. The increased current incollector 53. of transistor 35 causes that collector voltage and thevoltage. at the base 55 of transistor 57 to decrease. The decreased basevoltage at the PNP transistor 57 causes. that transistor also toincrease its conductance.

The increased conductance of transistor 57 will causean increased.current in the base 65 of the power transistor 15.through, the diode 67.The increased base current of power transistor 15 causes this transistorto increaseits conductance and thereby decrease-its impedance. The

lowerimpedance of transistor-15 in the line between the input terminallland the output terminal 19 causes a smaller voltagednop in the line thanthere had been under nominal operation. Consequently having a smallervolt age drop in the line, the output, voltage tends to rise toward thehigher input voltage.

If the output voltage had increased rather than decreased, the circuitwould have operated just in the re verse of that described for adecrease in output voltage. Thetransistors 31 and 35 are shown in such amanner that: their temperature coefficients compensate for each other solong as they both nominally operate in the same range. Thisis truebecause the output voltage is equal to the sum of the voltages on. thezener diodes 51 and 75 added to the voltage across the portion of thepotentiometer 45 between the zener diodes 51 and the wiper 43 plus thedifference in the base to emitter voltages of the transistors 31 and 35.As the base to emitter voltages change with temperature, theirdifference remains essentially constant. The transistor 31 has itscollector 39 connected directly to the output terminal 19 consequently anominal current is determined by the value of the resistor 37 land theline setting of the potentiometer 45. On the other hand, the collector53 of transistor 35 is connected to any desired value.

operation may be in the same range as that of transistor 31. The,additional means asshown is by theuse of PNP transistor 81 whosecollector 83 is connected to the collector 53 of the NPN transistor 35.The required addi-',

tional current then can be determined by aifixing values to theresistance 87 and thez ener diode 93.

In order to start the regulator, some voltage'must be applied atthe'base 71 of the transistor 35 and this voltage V is applied throughthe resistor 73. To preventa shunting of current lawaytrom the base 71ofthe transistor 35,521

diode 77 is placed in'linetwith the resistor 79. This diode serves nofunction afterftransistor 15 is conducting p p ya 1 The uses "of thezener'diodes '51, and 75 are twofold. First, they apply a source ofreference potential and sec- 0nd and more important, they, can bearranged in series groups so that the overall temperature coeflicient iszero. This can be accomplished by selecting allsz ero coefficient diodesor by combinations of positive andnegative coefiicient diodes such thatthe combination has a Zero temperature coefficient. Also, since diodebias current is incidentalto the operation of the supply, it can beadjusted This hecomesximportant'in the use of silicon diodes asreference elements as their temperature coeflicient can be varied by theamount of bias current flowing through them.

current through the diodes. Consequently, it is important to keep thecurrent through the diodes at a relatively 35 constant value. Touse thediodes in a feedback path,,it is necesary to vary the current throughthem in order to vary the conductance ofthe transistors 3 l and '35-. Tominimize the client of such feedback current, the resistors 49 and 79'are placed in series with the zener diodes 5-1 and 7 5. '.The currentthrough the diodes then is determined primarily by the values of theresistances 49 and 7 9' and such value of current is chosen to berelatively large in comparison with the change in. current due to thefeed back circuit. Temperature compensation for the transistor 57 isobtained by the, use of the resistor, 69 in conjunction with thezenerdiode 67. As temperature in creases, the emitter: current oftransistor 57 increases.- Thezener diode 67, having a positivetemperature coeffi cient, increases. in voltage thereby causing morecurrent to be delivered to the emitter 63 of transistor 57 by way ofresistor F69; The net'result is to maintain constant'base current totransistor 15 with changes in temperature. Thermal run-way of transistor15 is prevented by the voltage 66 and resistor 68. I This voltagesupplies reverse base current to the transistor 15, thereby compensatingfor the thermal leakage current of this transistor.

The capacitors 97 and 99 are placed across the zener diodes '51 and 75to overcomehigh frequency transients and thehighfrequency noise inherentto the diodes themselves.

The temperature coe flicient crossover points of zener,

The purpose of resistor 61 is to make the supply short circuit proof.This resistor 61 1,togcther with the input voltage 11 limits the flow ofCurrent at the output to'a" maximum value. This value can be set toprotect the power supply from overloads.

The embodiment described herein is for a positive power supply. In theevent that a negative power supply would be more desirable, the desiredresult can be obtained by a few simple changes in the circuit. To obtainthis, all NP'N and PNP transistors are reversed, to PNP and NP Ntransistors respectively. The input voltage polarities are reversed, andthe polarity of all the diodes are reversed. The circuit configurationremains the same.

The output impedance of the power supply is made very nearly purelyresistive for all frequencies of loading by the following method. Theresponse of the slowest transistor, the series element :15, isconsidered as an inductance L in series with the resistive outputimpedance R This series combination is in parallel with the outputcapacitor 101 and its effective series resistance R Now, if

then the output impedance will be purely resistive for all frequenciesof loading.

In general, while we have shown certain specific embodiments of ourinvention, it is to be understood that this is for the purpose ofillustration only and that our. invention is to be limited only by thescope of the appended claims.

We claim: 1. A voltage regulating circuit comprising a variableimpedance means in series with the output of said regucontrol terminalof the other said amplifying means being connected into the seriescircuit including the other of said constant voltage drop means, theoutput of the first said amplifying means being connected to a similarterminal of the second said amplifying means, the output of the secondsaid amplifying means being operably connected to said variation means,and an additional current amplifying means having a control terminal,the output of said additional current amplifying means being alsoconnected to the output of second said amplifying means, the controlterminal of said additional current amplifying means being connected tothe unregulated side of said voltage regulator. I

2. A voltage regulation circuit as described in claim 1 wherein saidconstant voltage drop means are zener diodes.

3. A voltage regulation circuit as described in claim 1 wherein saidconstant voltage drop means are silicon diodes.

4. A voltage regulation circuit as described in claim 1 wherein saidconstant voltage drop means are a combination of zener diodes andsilicon diodes.

5. A voltage regulating circuit as described in claim 1 wherein a secondimpedance means is connected between the output of said secondamplifying means and the input of said regulating circuit.

6. A temperature compensated voltage regulator com prising a variableimpedance in series with the output of said regulator, a first and asecond transistor each having two current terminals and a controlterminal, a current terminal of each being connected to thecorresponding terminal of the other and one side of said output, theother of said current terminals of the first said transistor connectedto the other side of said output, a first and a second series circuiteach comprising a constant voltage drop means and a resistance connectedacross said output with said resistances being connected to alternatesides of said output, the control terminal of one of said transistorsbeing connected to the junction of one of said constant voltage dropmeans and its respective resistance, the control term-mal of the otherof said transistors being connected into the series circuit includingthe other of said constant voltage drop means, a third transistor havingtwo current terminals and a control terminal, the control terminal ofsaid third transistor being connected to the other of said currentterminals of said second transistor, a current limiting means connectedto one of said current terminals of said third transistor, a constantvoltage drop means having a temperature coefficient connecting the othercurrent terminal of said third transistor to said variable impedance toadjust said variableimpedance, a current limiting device connecting theother said current terminal of said third transistor to the unregulatedside of said regulator.

7. A voltage regulation circuit as described in claim 6 wherein saidconstant voltage drop means are zener diodes.

8. A voltage regulation circuit as described in claim 6 wherein saidconstant voltage drop means are silicon diodes.

9. A voltageregulation circuit as described in claim 6 wherein saidconstant voltage drop means are a combination of zener diodes andsilicon diodes.

10. A voltage regulation circuit as described in claim 6 wherein afourth transistor having two current terminals and a control terminalhas one of its current terminals also connected to the other of saidcurrent terminals of said second transistor, the control terminal ofsaid fourth transistor being connected to the unregulated side of saidvoltage regulator.

11. A temperature compensated voltage regulating circuit comprisingdetection means for detecting variations in output voltage, a firstamplifying means coupled to said detection means for amplifying thedetected variations, inverting means coupled to said amplifying meansfor inverting the amplified variations, a first impedance meansconnected in series with said inverting means to provide a current pathfrom said inverting means whereby the current in said inverting meanscan be equalized with the current in said first amplifying means, asecond amplifying means coupled to said inverting means tor amplifyingsaid inverted variations and a second impedance means coupled to saidsecond amplifying means, said second impedance being connected betweenthe input and output of said regulating circuit.

12. A voltage regulator comprising, a pair of signal input terminals, apair of signal output terminals, a transistor connected in seriesbetween one of said pair of signal input terminals and one of said pairof signal output terminals for controlling the current flowtherebetween, a first network including a low impedance elementconnected between said signal output terminals for providing a .firstpoint of reference potential of low impedance which varies in accordancewith variations in the potential difference between said signal outputterminals, a second network connected between said signal outputterminals for providing a second point of reference potential which issubstantially constant in spite of variations in the potentialdifference between said signal output terminals, a differentialcomparator amplifier including a plurality of transistors connected toconduct through a common resistor and coupled to said first and secondpoints of reference potential for providing an error signalrepresentative of variations in the potential difference between saidsignal output terminals, and an error signal amplifier coupled betweensaid comparator amplifier and said transistor for controlling thecurrent flow of said transistor in response to said error signals andfor limiting the current through said transistor to a selected maximumvalue when the potential difierence between said signal output terminalsbecomes Zero, whereby said tranof a direct short of the signal outputterminals.

. 13; A voltage regulatorlas defined in claim 12 wherein said secondnetwork includes an impedance element and a zener diode connected inseries, said second point of reference potential being the commonjunction of said element and diode.

14. A voltage regulator as defined in claim 12 wherein a currentamplifier having a control terminal is coupled 7 '8 to said comparatoramplifier; the control terminal being connected to one of said pair ofsigna linput terminals.

References Cited in the file of this patent UNITED STATES PATENTS2,274,365 Gardiner Feb. 24, 1942 2,915,693, 7 Harrison Decul, 1959,2,963,637 Osborn Dec. '6, 1960

1. A VOLTAGE REGULATING CIRCUIT COMPRISING A VARIABLE IMPEDANCE MEANS IN SERIES WITH THE OUTPUT OF SAID REGULATING CIRCUIT, VARIATION MEANS FOR VARYING SAID IMPEDANCE MEANS, A FIRST AND A SECOND CONSTANT VOLTAGE DROP MEANS, EACH HAVING AN ADDITIONAL IMPEDANCE IN SERIES THEREWITH ACROSS SAID OUTPUT, SAID ADDITIONAL IMPEDANCES BEING CONNECTED TO DIFFERENT SIDES OF SAID OUTPUT, A FIRST AND A SECOND CURRENT AMPLIFYING MEANS, EACH HAVING A CONTROL TERMINAL, THE CONTROL TERMINAL OF ONE OF SAID AMPLIFYING MEANS BEING CONNECTED TO THE JUNCTION OF ONE OF SAID CONSTANT VOLTAGE DROP MEANS AND ITS RESPECTIVE ADDITIONAL IMPEDANCE, THE CONTROL TERMINAL OF THE OTHER SAID AMPLIFYING MEANS BEING CONNECTED INTO THE SERIES CIRCUIT INCLUDING THE OTHER OF SAID CONSTANT VOLTAGE DROP MEANS, THE OUTPUT OF THE FIRST SAID AMPLIFYING MEANS BEING CONNECTED TO A SIMILAR TERMINAL OF THE SECOND SAID AMPLIFYING MEANS, THE OUTPUT OF THE SECOND SAID AMPLIFYING MEANS BEING OPERABLY CONNECTED TO SAID VARIATION MEANS, AND AN ADDITIONAL CURRENT AMPLIFYING MEANS HAVING A CONTROL TERMINAL, THE OUTPUT OF SAID ADDITIONAL CURRENT AMPLIFYING MEANS BEING ALSO CONNECTED TO THE OUTPUT OF SECOND SAID AMPLIFYING MEANS, THE CONTROL TERMINAL OF SAID ADDITIONAL CURRENT AMPLIFYING MEANS BEING CONNECTED TO THE UNREGULATED SIDE OF SAID VOLTAGE REGULATOR. 